1. Field of the Invention
The instant invention relates generally to idler roll assemblies for absorbing the impact forces imposed thereupon by the dumping of loads of stone, coal, ore or the like upon the upper run of an endless conveyor belt entrained over the idler roll assemblies.
2. Prior Art
The desirability of providing a longlived, yet inexpensive impact absorbing idler roll assembly that (1) is positively secured to a central support shaft in a wobble-free manner, and (2) maintains maximum contact with the belt to prevent localized sagging has long been recognized within the conveyor industry. Similarly, the desirability of providing a shock absorbing idler roll that (3) is sufficiently sturdy and abrasion resistant to withstand the repeated application of heavy loads, yet resilient enough to yield momentarily and return to its unstressed configuration promptly, while (4) maintaining axial alignment between adjacent discs, has long been recognized. Numerous attempts have been made to attain all four of these desirable criteria in a preferred idler roll assembly configuration, but, to date, no assembly has fully satisfied every criteria.
To illustrate, U.S. Pat. No. 2,596,499, granted May 13, 1952 to S. M. Mercier, discloses an impact absorbing idler roll assembly comprised of a plurality of readily resilient tires, or discs, stacked on a tubular shell. An annular opening is formed in the hub of each tire so that the tire may be seated on a cylindrical shaft extending axially through the roll. Projections on one side of each tire engage recesses on the opposite side of the adjacent tire so that the tires can be interlocked with one another.
U.S. Pat. No. 2,632,560, granted Mar. 24, 1953 to F. J. Wright, discloses an impact absorbing idler roll assembly comprised of a plurality of tires, each tire or disc having a tubular hub sleeve that enables it to be mounted upon an axially extending tubular support hub. Each tire has a tapered resilient body portion whose axial dimension is greatest adjacent to the tubular support hub, and a substantially non-deformable rim is joined to the periphery of each tire. A tie rod extends through the tubular support hub, and nuts on the opposite ends of the rod are tightened to hold the asssembly in alignment.
U.S. Pat. No. 3,310,160, granted Mar. 21, 1967 to D. C. Reilly, discloses an impact absorbing idler roll assembly comprised of a plurality of tires, or discs, secured upon a cylindrical shell that can rotate relative to a cylindrical shaft disposed within the shell. Each tire includes a hub with an annular opening that slips onto the hollow cylindrical shell for rotation about a fixed central shaft, a resilient tube body, and a tread that extends about the circumference of the tire. Axially extending jaw teeth are formed on the hub of each tire, so that the teeth of adjacent tires can be interlocked and the tires can rotate as a unit. Retaining rings with radially extending setscrews are employed at opposite ends of the roller so that the tires are retained in the desired axial alignment upon the hollow cylindrical shell.
However, each of the three illustrative impact absorbing idler roll assemblies noted above, failed to satisfy one or more of the criteria for optimum efficiency previously set forth. Perhaps, the most significant shortcoming encountered with all three of the illustrative assemblies was angular slippage of the tires or discs relative to the support shaft upon which are mounted; this shortcoming was attributable to the ease with which the annular hub of the disc rode along the cylindrical surface of the support shaft. Such slippage lead to increased wear on the bearings of the idler assembly with the potential attendant generation of internal heat and friction; also, since certain tires or discs rotated easily while others did not, localized shearing forces were produced that adversely affected the conveyor belt passing over the idler roll assembly.
Also, the use of several distinct materials in the fabrication of the impact absorbing idler roll assembly proposed in the Wright patent could introduce an undersirable cost factor into the total production costs for such assembly. Furthermore, the use of tires having rims that are much thinner than their hubs allows relatively wide expanses of the belt to be unsupported; consequently, the belt will tend to sag and wear unevenly.